Coming from a 10 dan who:
last week had 2 days in a row of rank 3, has had 2 days in a row of rank 2, and has had 3 days in a row of rank 5;
Rank and belt means absolutely NOTHING. Even though I sometimes ave good ranks, and I am high belt, I will admit they don't mean a thing. Those ranks can be easily obtained through some decent streaks on a day where much of the community was inactive. And also, the belt isn't wins, it plays. Sure you get better with experience, but it still doesn't mean much. There are some people of my belt who are incredible, there are some people who, to be perfectly honest, play like a blue belt...
Also, some people might be incredible at one mode, like wushu, but terrible at another, like judo. So that's another reason you really can't say based on belt; depends on the mode and their specialties.